Stoichiometry

Question 1

Define empirical formula.

Answer 1

The simplest whole number ratio between the number of atoms of each element making up a compound.

Question 2

Define molecular formula?

Answer 2

The exact number of different atoms making up a molecule.

Question 3

What is avogadro’s constant?

Answer 3

the number of atoms in 12 grams of the most abundant isotope of carbon (6.02 x 10²³)

Question 4

What is gram-molecular weight?

Answer 4

The weight in grams of a mole of molecules of a given element.

Question 5

What is the equation to work out moles?

Answer 5

Moles = mass/mr

Question 6

What are the steps to obtain empirical formula?

Answer 6

1) divide % composition by GAW of the element to calculate moles of each element
2) divide number of moles of each element by the smallest number of moles
3) multiply the numbers in the ratio to create a whole number ratio

Question 7

What is the sum of all oxidation numbers in a neutral molecule?

Answer 7

0

Question 8

What are the common oxidation states to memorise?

Answer 8

Hydrogen => +1

Oxygen => -2 in most compounds
exceptions are: peroxides (-1), superoxides (-1/2), OF₂ (+2)

Alkali metals (1st column in period table) = +1

Alkaline earth metals (2nd column in period table) = +2

Aluminium = +3